Alteration of the calcium content in inner hair cells of the cochlea of the guinea pig after acute noise trauma with and without application of the organic calcium channel blocker diltiazem

Calcium ions are known to be important to the process of signal transductio n across the apical and basal sides of the inner hair cells. Calcium channe l antagonists have been demonstrated by light microscopy to provide protect ion against acoustic trauma. To evaluate the protective effect of calcium c hannel blocker on the inner ear cells to noise exposure, the amount of the histochemical reaction products formed in the cytoplasm of the inner hair c ells of the guinea pig after application of pyroantimonate was measured by an image processing system connected to an energy-filtering transmission el ectron microscope (EFTEM). Compared to untreated control specimens (experim ental animal group I) the amount of precipitable calcium had clearly increa sed in the inner hair cells of noise-exposed cochleae 60 h after an acute n oise trauma (group III). In addition, small electron-lucent areas could be identified in the cytoplasm of the hair cells probably representing damage to the cellular fine structure. When the calcium channel blocker diltiazem was administered without any additional noise exposure the calcium content was drastically reduced in the inner hair cells (group II), but when the an tagonist was given before and after acute noise trauma (group IV), the calc ium content in the inner hair cells was nearly compared to the amount deter mined in the untreated group of animals. The role of diltiazem is discussed in respect of tissue protection and to the maintenance of the calcium-depe ndent physiological processes in the inner hair cells during signal transdu ction.